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Message-ID: <e7614b27-e9b4-49a8-831b-0acd33911336@amd.com>
Date: Tue, 18 Mar 2025 19:25:42 +0800
From: "Huang, Honglei1" <Honglei1.Huang@....com>
To: Gurchetan Singh <gurchetansingh@...omium.org>
Cc: Demi Marie Obenour <demiobenour@...il.com>,
David Airlie <airlied@...hat.com>, Gerd Hoffmann <kraxel@...hat.com>,
Chia-I Wu <olvaffe@...il.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
Simona Vetter <simona@...ll.ch>, Rob Clark <robdclark@...il.com>,
Huang Rui <ray.huang@....com>, dri-devel@...ts.freedesktop.org,
virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
Dmitry Osipenko <dmitry.osipenko@...labora.com>
Subject: Re: [PATCH v1 1/7] virtio-gpu api: add blob userptr resource
On 2025/3/18 9:37, Gurchetan Singh wrote:
>
>
> On Thu, Mar 6, 2025 at 2:52 AM Huang, Honglei1 <Honglei1.Huang@....com
> <mailto:Honglei1.Huang@....com>> wrote:
>
>
> On 2025/3/1 5:21, Demi Marie Obenour wrote:
> > On 2/28/25 12:36 AM, Honglei Huang wrote:
> >> From: Honglei Huang <Honglei1.Huang@....com
> <mailto:Honglei1.Huang@....com>>
> >>
> >> Add a new resource for blob resource, called userptr, used for let
> >> host access guest user space memory, to acquire buffer based userptr
> >> feature in virtio GPU.
> >>
> >> - The capset VIRTIO_GPU_CAPSET_HSAKMT used for context init,
> >> in this series patches only HSAKMT context can use the userptr
> >> feature. HSAKMT is a GPU compute library in HSA stack, like
> >> the role libdrm in mesa stack.
> >
> > Userptr should not be limited to HSMKMT contexts. Userptr can
> > accelerate shm buffers by avoiding a copy from guest to host, and
> > it can be implemented using grant tables on Xen.
>
> Yes, I totally agree userptr can accelerate shm buffers, but I currently
> don't know if there are any other projects working on similar features,
> or if maintainers have any opinions or better ways to implement them, so
> I temporarily limit this feature to HSAKMT context only.
>
> I am waiting for everyone's opinions, please provide your thoughts.
>
>
> I wonder if you can emulate userptr using udmabuf on the host-side?
>
> Essentially for the guest, it'll be a malloc'ed memory, which means a
> guest sg list. We can convert the guest sg-list to udmabuf using well-
> known mechanisms on the host side. I hope amdkfd can operate on dma-
> bufs too?
>
> I do such a feature that would have a more generic utility outside of
> HSAKMT contexts and not rely on Xen-specific grant tables ...
> checkout VIRTIO_GPU_BLOB_FLAG_CREATE_GUEST_HANDLE in crosvm for an example.
I think userptr can be emulated by udmabuf if the sg list is from guest
user sapce and not moveable, amdkfd can operate dma-buf, and the userptr
feature can be achieved by partial functions of dma-buf as far as I can see.
But the udmabuf need managed by UMD, this will result in some
performance loss, and we are planning to implement virtio GPU userptr
using hmm_rang_fault, udmabuf solution may be completely different from
this one.
I saw the feature VIRTIO_GPU_BLOB_FLAG_CREATE_GUEST_HANDLE is used by
the crosvm in beta branch, but I can not find the kernel virtio gpu
part, how to access it? Maybe I can try or help.
>
>
>
> Regards,
> Honglei
>
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